1. Field of the Invention
This invention relates to an X-ray diode source for flash radiography.
2. Description of the Related Art
Flash radiography is a technique used to take stop-action pictures of dynamic events. Such dynamic events may include detonation of high explosives or implosion of a mock weapon assembly containing a surrogate material to represent a nuclear core. An apparatus for flash radiography uses one or more diodes to generate a short X-ray pulse. Transmitted flux from a number of X-ray photons per unit area is then recorded on a shielded detector. Diodes useful for flash radiography produce an intense electron beam, which efficiently propagates beam energy along an anode. The efficient propagation of an intense electron beam is highly desirable for many reasons. One advantage is application of beam energy from a sufficient distance to avoid damage to the power source. Another advantage is an ability to confine a target to a specific location. Such features may enable irradiation of a solid target pellet for material response studies, produce and heat high-temperature plasmas and produce an intense localized source of X rays.
Existing devices for producing an intense flow of electrons include the dielectric-rod-cathode diode (Bennett diode), planar and hemispherical pinched electron-beam diodes and planar diodes with exploding wires on axis. These devices propagate electron beams with relatively low efficiency. Other techniques for propagating beams include exploding-wire discharge channels, z-pinch discharge guides and laser-initiated discharges. These techniques guide a beam through a preformed plasma discharge. A propagation efficiency reported for these techniques, however, does not exceed 50%. Moreover, these techniques usually require large, expensive and complex external equipment.
Pinch propagation along rod--and cylindrical-shaped anodes of a diode for producing a multimicrosecond pulse of X rays has been observed by K. F. Zelenskii, O. P. Pecherskii, and V. A. Tsukerman (Soviet Physics-Technical Physics, Vol. 13, No. 9, March, 1969, pp 1284-1289). The Zelenskii device operates at high impedance (approximately 200 ohms) and the anode includes a cylinder having either a small constant radius providing a slow pinch formation and very low currents or a large constant radius resulting in higher current but comparatively slow pinch propagation and low current density. Although the Zelenskii device forms an anode surface plasma, the anode, because of its shape and material, may not produce high ion fluxes, form and propagate fast pinch or operate at low impedance.